Ethanol alleviates glucose stress from Euglena gracilis

Euglena gracilis, a microalga, can be cultured under photoautotrophic, heterotrophic, or mixotrophic conditions. This species can produce proteins, vitamins, and lipids. Based on previous reports, paramylon, a storage polysaccharide of E. gracilis and a type of β-1,3-glucan, can inhibit the development of skin lesions. Glucose increases the proliferation of E. gracilis and the accumulation of paramylon. However, excess glucose decreases the proliferation of E. gracilis because of high osmotic pressure. In this study, we found that E. gracilis cells cultured with high concentrations of glucose became hypertrophied rather than dehydrated and shrunken. The addition of ethanol (concentration of 0.5%) improved the proliferation of E. gracilis under a high glucose concentration of 400 mM. The addition of ethanol resulted in spindle-shaped cells similar to those observed under a no-glucose condition. These results indicate that ethanol alleviates glucose stress in E. gracilis, revealing the physiological aspects of E. gracilis under heterotrophic conditions.